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/*
* COPYRIGHT (c) 2019 Chris Johns <chrisj@rtems.org>
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.org/license/LICENSE.
*/
/**
* @file
*
* @ingroup rtems_rtl
*
* @brief RTEMS Run-Time Linker Object File Trampoline Relocations Table.
*
* Cache relocation records that could result in a trampoline. The unresolved
* symbol table holds variable the symbol name (length string) and the object
* file's relocation records that reference the unresolved symbol. The
* trampoline cache is an extension to this table to reuse the code and memory
* and support trampolines.
*
* Some architectures require trampolines or veneers to extend the range of
* some instructions. The compiler generates small optimized instructions
* assuming most destinations are within the range of the instruction. The
* instructions are smaller in size and can have a number of encodings with
* different ranges. If a relocation record points to a symbol that is out of
* range for the instruction a trampoline is used to extend the instruction's
* range. A trampoline is a small fragment of architecture specific
* instructions located within the range of the relocation record instruction
* that can reach the entire address range. The trampoline's execution is
* transparent to the execution of the object file.
*
* An object file that needs a trampoline has a table allocated close to the
* text section. It has to be close to ensure the largest possible object file
* can be spported. The number of slots in a table depends on:
*
* # Location of the code
* # The type of relocation records in the object file
* # The instruction encoding the relocation record points too
* # The landing address of the instruction
*
* The allocation of the text segment and the trampoline table have to happen
* with the allocator lock being locked and held to make sure no other
* allocations happen inbetween the text section allocation and the trampoline
* table. Holding an allocator lock limits what the link editor can do when
* when the default heap allocator is being used. If calls any operating
* system services including the file system use the same allocator a deadlock
* will occur. This creates a conflict between performing the allocations
* together and reading the instructions while holding the allocator lock.
*
* The trampoline cache holds the parsed relocation records that could result
* in a trampoline. These records can be exaimined after the allocation of the
* text segment to determine how many relocation record target's are out of
* range. The minimum range for a specific type of relocation record has to be
* used as the instructions cannot be loaded.
*/
#if !defined (_RTEMS_RTL_TRAMPOLINE_H_)
#define _RTEMS_RTL_TRAMPOLINE_H_
#include <rtems/rtl/rtl-unresolved.h>
#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */
/**
* Add a relocation to the list of trampolinr relocations.
*
* @param obj The object table the relocation record is for.
* @param flags Format specific flags.
* @param sect The target section number the relocation references.
* @param symvalue The symbol's value.
* @param rel The format specific relocation data.
* @retval true The relocation has been added.
* @retval false The relocation could not be added.
*/
bool rtems_rtl_trampoline_add (rtems_rtl_obj* obj,
const uint16_t flags,
const uint16_t sect,
const rtems_rtl_word symvalue,
const rtems_rtl_word* rel);
/**
* Remove the relocation records for an object file.
*
* @param obj The object table the symbols are for.
*/
void rtems_rtl_trampoline_remove (rtems_rtl_obj* obj);
#ifdef __cplusplus
}
#endif /* __cplusplus */
#endif
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